Text / Engineering Techniques for Condit Dam Removal

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Title: Engineering Techniques for Condit Dam Removal
Alternative Title: Managing Watersheds for Human and Natural Impacts: Engineering, Ecological, and Economic Challenges, EWRI and ASCE 2005 Watershed Management Conference, Williamsburg, Virginia, July 19-22, 2005
Creator: Dennis Gathard
G&G Associates, Seattle, WA
Date Created and/or Issued: 2005
Contributing Institution: UC Riverside, Library, Water Resources Collections and Archives
Collection: Clearinghouse for Dam Removal Information (CDRI)
Rights Information: Copyrighted
Transmission or reproduction of materials protected by copyright beyond that allowed by fair use requires the written permission of the copyright owners. Works not in the public domain cannot be commercially exploited without permission of the copyright owner. Responsibility for any use rests exclusively with the user.
Description: Scope/Content: Abstract: The Condit Hydroelectric Project is owned and operated by PacifiCorp. The 125 foot tall concrete dam is located on the White Salmon River approximately 3 miles upstream of the confluence with the Columbia River near Bingen, Washington. PacifiCorp has decided as part of the relicensing process for the project to remove the dam and appurtenant structures. The decision to remove the dam has been approved by the FERC. The removal project is currently in the permitting stage of the process. Several similar large concrete dams removal project in the western United States are currently under investigation (Elwha, Glines Canyon and Matilija dams). Estimated removal costs for Condit are well below costs for other similar dam removal projects due to rapid removal techniques and limited mitigation requirements. The approach to river diversion and structure removal at several other dam removal projects involves notching the dam from the top to divert river flow and control of sediment releases. The notching removal approach results in increased costs relative to the approaches for sediment management and structure removal for Condit Dam. Removal of the concrete structure will be rapidly conducted in dry conditions, using drilling and blasting techniques, by constructing an opening in the bottom of the dam to rapidly drain the reservoir and allow river flow to pass below construction activities. Pre-drilling and blasting an 12 by 18 foot hole at the lowest feasible elevation will be used to construct the river by-pass tunnel. Containment and removal of concrete after blasting will be aided by using exterior concrete while interior sections are blasted into rubble sized material for easy removal. Sediment removal will be accomplished using natural river flow and rapid drawdown techniques. Natural river flow will transport over 1.57 million cubic yards of the approximately 2.2 million cubic yards of trapped sediment out of the reservoir area in the first year after tunnel construction. Most of the sediment will erode in the first week after the dam is breached. Sediment will erode into the White Salmon River that flows into the Columbia River. Most of the eroded sediment will be transported in suspension in the water column. Most of the sediment will deposit in the mouth of the White Salmon River.
Scope/Content: Height: 125 Length: 250
Scope/Content: Date constructed: 1913.
Type: text
Form/Genre: digital copy
Identifier: ark:/86086/n2tb16jw
119
Subject: Sediment and channel dynamics
Dams
Dam retirement
Place: Columbia River, WA
White Salmon River, WA
Condit Dam
US

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